Numerous varieties of fasteners have been developed in response to the diversity of applications for which fasteners can be used. As manufacturing processes become more automated, there has been an increased emphasis on developing fasteners which simplify and facilitate assembly, yet which are capable of reliably securing the particular members being joined. Such a need exists in the electronic industry for the purpose of reliably securing circuit boards to the support frame or chassis of electronic enclosures, cabinets and casings. Fasteners for this type of application generally must be capable of being installed without damage to the circuit board and chassis, yet must also provide secure and reliable attachment so as ensure sufficient vibration resistance.
Generally, the particular type of fastener suitable for a given task is heavily dependent upon the characteristics of the structures being joined, such as their relative thicknesses and materials, the method of installation, and whether the joint is intended to be permanent or temporary. Conventionally, threaded fasteners are widely used to secure circuit boards to a chassis, at times incorporating a self-locking feature to discourage the fastener from becoming loose due to vibration. However, a significant disadvantage associated with the use of threaded fasteners is that they require a rotational motion for installation. In terms of automated assembly methods, those that require a rotational motion add significant costs to the assembly process. When manual assembly methods are used, threaded fasteners are often undesirable in that carpal tunnel syndrome has been linked to the ratcheting motion required to install such fasteners. In addition, it is desirable to avoid the relatively greater weight and costs associated with threaded fasteners.
For joining thin panel-like members such as a circuit board and chassis, various approaches have been suggested which often employ some type of expandable feature. Such features have long been used to secure two panels together, as illustrated by the snap fastener of U.S. Pat. No. 2,327,328 to Murphy. However, fasteners of this type are not suitable for securing a circuit board to a chassis, in that the snap fastener can be easily disengaged, and the clamping force generated by the snap ring is generally uncontrollable and often insufficient to resistant vibration.
U.S. Pat. No. 4,122,583 to Grittner et al. teaches a mechanically expandable fastening clip which is intended for securing an interior trim panel to the body panel of a vehicle. However, the fastening clip taught by Grittner et al. is not generally suitable for securing a circuit board to a chassis, in that after assembly, the circuit board and chassis are spaced apart instead of being held in intimate contact, making the circuit board more susceptible to vibration. Furthermore, the fastening clip is rather complicated in its construction, and must be pre-assembled to the circuit board. Furthermore, the clip is not readily reusable, in that the expandable portion of the clip is likely to be plastically deformed during removal of the fastener.
Numerous forms of fasteners incorporating an expandable feature have been specifically suggested for use in the electronics industry to secure a circuit board to a chassis. Generally, however, such prior art fasteners have several disadvantages, including the inability to be removed without access to both sides of the circuit board, clamping loads which are not readily controllable, excessive weight or size, and excessive forces required for installation.
Thus, it would be desirable to provide a relatively low cost, reusable fastener for joining together two or more relatively thin members, such as a circuit board and a support chassis, wherein the fastener can be easily installed manually or with the use of automated equipment without involving a rotational motion. Further, the fastener should be capable of maintaining intimate contact between the members, and readily removable to allow separation of the members. In addition, the fastener should be capable of generating a predeterminable clamping load, while also being relatively light weight and inexpensive.